Work over the past several years has brought us to the verge of a realistic electrical equivalent circuit model for the plasma membrane of Neurospora. The model incorporates a sigmoidal current-voltage relatonship for the primary H ion extrusion pump, a hyperbolic I-V relationship for the aggregate of secondary (ion-coupled) transport systems, and a linear (ohmic) I-V curve for the "leaks". The definitive presentation of this equivalent circuit, along with a detailed I-V analysis of two component transport systems (the proton pump, and the hexose/H ion cotransport system) will be published in the coming year. In addition, two major new departures will be made. 1) Determination of the intracellular pH of Neurospora, and its relationship to the driving force for several transport systems, to the overall current-voltage relationships for those systems, and to various metabolic shifts. These experiments will use recessed-tip microelectrodes for measuring intracellular pH, backed up by 31P NMR spectroscopy. They will also use a programmed fast-scan to obtain the membrane current-voltage relationship under various transient and steady state conditions. 2) Determination of the relationship between transport and intracellular cyclic nucleotide behavior in Neurospora. This will use a combined biochemical and electrophysiological approach.